Remind me when you "see a sun rising in the morning" next time. Using an indefinite article here is noticed by the reader and will pose the question "Oh, is there one more?". In language rules are sometimes not as absolute as "all definite articles can also be indefinite".
This is not a proper comparison, as the relevant property is not of something being the only member of a category, but of being the already mentioned one.
For the sun we suppose the person speaking knows of THE Sun. For the supermassive black hole at the center of the galaxy we don't.
This can be easily shown as "The Black Hole Threw a Star Out of the Milky Way Galaxy" is clearly misusing the definite article.
"The Black Hole at the Center of the Milky Way Threw a Star Out of the Galaxy" would probably be an alternate way to write the headline using the definite article.
Agree that _just_ an article swap leaves the headline worse off.
I agree this is a better headline. In the original, I was left wondering if it was possible for a black hole outside of our Galaxy to eject a star from ours.
I agree. Also, the average reader of NYT doesn't care or know about the giant black hole at the center of our galaxy and 'black hole' is enough for them to get the point of the story.
